1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly to a method and an apparatus for transmitting and receiving information using a random access code in a random access procedure.
2. Description of the Related Art
A Universal Mobile Telecommunication Service (UMTS) system is a 3rd Generation (3G) asynchronous mobile communication system, which uses wideband Code Division Multiple Access (CDMA) and is based on Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS), which are European mobile communication systems. In the third generation Partnership Project (3GPP), which is in charge of standardization of the UMTS, active discussion is underway regarding Long Term Evolution (LTE) of the UMTS system. The LTE is a technology which targets commercialization thereof by the year 2010 and the realization of high speed packet-based communication at about 100 Mbps. To this end, various schemes are being discussed, such as reducing the number of nodes located in communication paths by simplifying the structure of a network, and approaching a wireless protocol to a wireless channel as much as possible.
FIG. 1 illustrates a conventional evolved UMTS mobile communication system. As shown, an Evolved Radio Access Network (E-RAN) 110 or 112 has a simplified 2 node structure, which includes Evolved Node Bs (ENBs) 120, 122, 124, 126 and 128 and Anchor Nodes 130 and 132. A User Equipment (UE) 101 is connected to an Internet Protocol (IP) network 114 through the E-RANs 110 and 112.
The ENBs 120 to 128 correspond to legacy Node Bs of the UMTS system and are connected to the UE 101 through a wireless channel. The ENBs 120 to 128 perform more complex functions than the legacy Node B. In the LTE, all user traffic including the real-time service, such as Voice over IP (VoIP) using the Internet protocol, is provided through a shared channel. Therefore, the LTE requires an apparatus for collecting status information of UEs and performing scheduling by using the collected information. The ENBs 120 to 128 control of the scheduling.
Usually, one ENB controls a plurality of cells and performs Adaptive Modulation and Coding (AMC), which determines a modulation scheme and a channel coding rate in accordance with the channel status of a UE. As in the High Speed Uplink Packet Access (HSUPA; which is also called “Enhanced Dedicated Channel (E-DHC)”) and the High Speed Downlink Packet Access (HSDPA) of the UMTS, the Hybrid Automatic Repeat Request (HARQ) is performed between the ENBs 120 to 128 and the UE 101 in the LTE.
Because it is impossible for only the HARQ to satisfy requirements for various Qualities of Service (QoSs), an outer Automatic Repeat Request (ARQ) in a higher layer may be performed between the UE 101 and the ENBs 120 to 128. The HARQ process refers to soft-combining previously-received data with retransmitted data without discarding the previously-received data, thereby improving the ratio of success in the reception, and is used to improve the transmission efficiency in the high speed packet communication, such as the HSDPA and the Enhanced Dedicated Channel (EDCH). In order to implement a maximum transmission speed of 100 Mbps, the LTE is expected to use Orthogonal Frequency Division Multiplexing (OFDM) in 20 MHz bandwidth as wireless connection technology.
In a mobile communication system such as the UMTS and the LTE, a Random Access (RA) procedure is used when a UE in a Radio Resource Control (RRC) idle mode or RRC-connected mode acquires UpLink (UL) timing synchronization with an ENB, and/or sets initial uplink transmission power, and/or requests an ENB or a higher (anchor) node to transmit an (initial) uplink message. The RRC idle mode and the RRC-connected mode are defined in the TR25.813 v700 standard of the 3GPP. In general, a status in which the ENB does not possess context information of a UE and controls location of a UE based on each Routing Area (RA) or Tracking Area (TA) for paging instead of controlling location of a UE based on each cell is called “an RRC idle mode”, and a status in which the ENB possesses context information of a UE, has an RRC connection set between the UE and the ENB, and can control location of a UE based on each cell, is called “an RRC-connected mode”.
The conventional random access procedure as described above requires technology for efficiently transmitting a message while preventing random access collision between UEs.